Objectives: 1. Biochemical factors involved in differentiation and development of tadpole liver. 2. Molecular effects of thyroxine as the inducer of the enzymes of urea biosynthesis. 3. Factors involved in the regulation of induction and levels of urea biosynthetic enzymes. 4. Rates of biosynthesis and degradation of the mitochondrial enzymes carbamyl phosphate synthetase and ornithine transcarbamylase, and the cytosol enzyme arginase, as influenced by thyroxine treatment of tadpoles. 5. Biochemical characterization of mitochondria and nature of processes involved in acquisition of mitochondrial enzymes synthesized by extramitochondrial ribosomes; mitochondriagenesis. 6. Effect of thyroxine on capacity of tadpole liver ribosomes to translate natural messenger RNA as compared with synthetic messenger RNA. 7. Subunits, peptide mapping, and mechanism of action of frog carbamyl phosphate synthetase, ornithine transcarbamylase and arginase.